Update documentation.

Author: Tomas Kirda

readme.md

@@ -14,7 +14,7 @@ The standard jquery.autocomplete.js file is around 2.7KB when minified via Closu
     * `options`: An object literal which defines the settings to use for the autocomplete plugin.
         * `serviceUrl`: Server side URL or callback function that returns serviceUrl string. Optional if local lookup data is provided.
         * `ajaxSettings`: Any additional [Ajax Settings](http://api.jquery.com/jquery.ajax/#jQuery-ajax-settings) that configure the jQuery Ajax request.
-        * `lookup`: Lookup array for the suggestions. It may be array of strings or `suggestion` object literals.
+        * `lookup`: Callback function or lookup array for the suggestions. It may be array of strings or `suggestion` object literals.
             * `suggestion`: An object literal with the following format: `{ value: 'string', data: any }`.
         * `lookupFilter`: `function (suggestion, query, queryLowerCase) {}` filter function for local lookups. By default it does partial string match (case insensitive).
         * `lookupLimit`: Number of maximum results to display for local lookup. Default: no limit.
@@ -115,6 +115,27 @@ $('#autocomplete').autocomplete({
 });
 ```
 
+Custom lookup function:
+```javascript
+
+$('#autocomplete').autocomplete({
+    lookup: function (query, done) {
+        // Do ajax call or lookup locally, when done,
+        // call the callback and pass your results:
+        var results = [
+            { "value": "United Arab Emirates", "data": "AE" },
+            { "value": "United Kingdom",       "data": "UK" },
+            { "value": "United States",        "data": "US" }
+        ];
+
+        done(results);
+    },
+    onSelect: function (suggestion) {
+        alert('You selected: ' + suggestion.value + ', ' + suggestion.data);
+    }
+});
+```
+
 ##Styling
 
 Generated HTML markup for suggestions is displayed bellow. You may style it any way you'd like.